This blog provides updated forecasts and comments on current weather or other topics

Thursday, September 9, 2010

The Long-Term Forecast

Many of you have asked for the details of the long-term forecast: what is expected for this fall and winter. OK, you asked for it--and some of you may not like what you hear.

The most powerful tool we have for predicting months ahead of time is the correlation between El Nino/ La Nina and Northwest weather. You have heard me talk about this frequently on this blog--the tropical Pacific sea surface temperatures oscillate between cooler than normal conditions (La Nina) and warmer than normal conditions (El Nino) over a period of roughly 3-7 years. And it turns out there is a strong correlation between the temperature of the tropical Pacific and the general character of our weather.

During the past half year the tropical Pacific has decidedly turned toward La Nina, with cooler than normal temperatures now evident near the equator. Here is the latest graphic: blue indicates more than .5C cooler than normal.

The figure below shows you the time evolution of this cold water...take a look at the Nino 3.4 area, a zone in the equatorial Pacific that is most often considered. Last year we had an El Nino (warm anomalies--an anomaly is the difference from normal) and during the early summer we rapidly slid into colder temps. We now have a moderate La Nina and it may well become a strong one. Computer models of La Nina evolution run by the National Weather Service and others are predicting a continuation of the La Nina through the winter.

Now the interesting thing is that the temperature of the tropical Pacific influences weather throughout the Northern Hemisphere, including us. Perhaps some day I will tell you why that happens, but in this blog let me give you the bottom line.

La Nina years are generally associated with wetter than normal conditions during the fall and winter, something I bet you believe after the last few days of liquid sunshine.

Here are official NWS average precipitation anomalies (again differences from normal) for fall and winter. The Northwest is wetter than normal in both, and you will note that California is relatively dry.Now what about temperature? Turns out there is little temperature signal for La Nina years during fall, but during winter (January-March) we are colder than normal, as shown in this graphic:So colder and wetter than normal in winter....what do you think that implies? Yes, more SNOW, particularly in the mountains (see the graphic, where blue indicates more snow than normal). A good year to risk a season pass at a local ski area.It also turns out that there is a greater probability of lowland snow west of the Cascades during La Nina years. Now, if Seattle's Mayor McGinn knows whats good for him he would be sharpening those snow plow blades, securing lots of sand and SALT, establishing rational plans for plowing the city, and telling all snow plow operators to avoid his neighborhood. We lost one Mayor to snowappocalypse, two would be an embarrassment. I offered to build a SNOWWATCH web page for the city...no bites yet.

Anything would be better than last winters perpetual boring fall like drival. It never got very cold, very wet or very warm it was just about as dull as dull can get for winters around here in the PNW. Looking at some of the things happening in our oceans and in our atmosphere this year it looks like thing could be interesting.

I PLAN on preparing. I PLAN on having my food storage filled out and my pantry built before we have to go through I-5 being flooded, AGAIN. In fact anyone can go to the LDS ( Mormon) cannery in Kent and buy flour, sugar, wheat, rice and other dry goods using a form found on lds.org under the heading family preparadness.

Hi Cliff,I'm just curious. To you knowledge, have we ever been in a "La Nina" year to where the PNW turned out to be drier & warmer than normal or an "El Nino" year where we were cooler & wetter than normal?Thanks.

LorbeerTLC, that probably happens more frequently than many people think. For example, the winter of 1999/2000 was very unremarkable for a La Nina winter. Temperatures were above average and there were next to no storms the entire winter. On the flipside, the winter of 2006/07 was a relatively cool and stormy El Nino. I don't think it was colder than normal, but it wasn't mild like a typical El Nino.

Sweet. Cliff, how do you think this La Nina will compare to that of 2007-2008? Cause that was a great year for skiing. I have a feeling this could be a real strong one, because the last MAJOR La Nina (1998-1999) occured right after one of the strongest El Ninos ever recorded. I think even an average snowfall in the mountains would make all skiers happy compared to last year.

Do you have any information on the interplay between La Nina and the Pacific Decadal Oscillation as it affects precipitation/temperature? In other words, is it known if the PDO results in an amplifying effect?

So we may be cooler and wetter than normal....but what about wind? Do big windstorms usually happen in La Nina years? Wondering if the 3 biggest in my memory...the Columbus Day Storm, Inagural Day Storm, and the most recent Hannuka Eve Storm....were on nuetral or La Nina years? OK...so I love a good wind storm! Snow is good too, but wind is so much more exciting!

Tim, spent time in Portland, the former director of transportation who coined that phrase was busted on her Vespa for DUI. Her campaign for city council is toast. Portland didn't fare any better the last go round when thousands were stuck on the freeway.

mainstreeter: Please let me know how that makes Seattle competent at anything other than building sports stadiums and sculpture parks. The World-Class City (TM) got schooled by pretty much all of its uncool plebeian neighbors during that snowstorm. I guess that's what happens when you put basic city services above impressing trendoids in Paris.

And you still apparently don't know the difference between condemnation and a warning.

Portland will be a near second to Seattle when the zombie plague spreads. iphones and the art of texting won't help both crowds when the #&*& hits the fan. If people are worried about not getting their latte because of a little snow on the roads we are in trouble.

So extra dark and drippy is the rule here, I see. Can you suggest the closest place to find warm saltwater come Jan/Feb and maybe a little sunshine? I can see my SAD self will need a few days there this winter. Baja? Hawaii? Florida?

Well, it's just winter we're talking about, not "30 Days of Night" or "I Am Legend." We've got our warning. Now let's USE it and while we're at it, let's encourage everyone else we know to prepare as well. The more people who heed the call that winter (or November) could be bad, the better, and maybe some of them will act on the warning. I know I am, I'm preparing now. Let's face it, we could all brush up on our preparedness, considering the other risks out there for living in a subduction zone. Then after we're prepped, and the snow falls, let's go sledding!

What about the PDO? Would be interested to hear what you expect from the really long-term forecast, i.e., next couple of decades. Have we figured out if we have entered a negative phase PDO and if so, should we expect more summers like this in the coming decades?